[SoM] Binding importer needs a mapping step

[stephen-hawley]

Right now there are a number of protocols that are being remapped by hand.
I fully expect that there will be a number that we are incorrectly mapping because apple decided to change the name in swift.

To address this, I think that there needs to be a subsystem that takes an input file with the form:

<remap>
    <entityNameRule platform="" entityType="" csFullName="" swiftModuleName="" swiftName=""/>
    <methodNameRule platform="" entityType="" csFullName="" csMethodName="" swiftName=""/>
    <methodParameterRule platform="" entityType="" csFullName="" csMethodName="">
        <parameter csName="" swiftName="" swiftTypeSpec="" isInOut=""/>
    </methodParameterRule>
</remap>

entityType would be one of Class, Struct, Protocol, Enum
platform would be one of iOS, macOS, tvOS, watchOS, * (or empty)
Each rule would match on an entity type for the given platform and match of the full C# name present.
Each matching rule would project the changes onto those entities.

When rules are read in, they can be put into separate containers based on entity type. This will likely speed up mapping since there are likely to be fewer class rules than protocol rules.

The mapping function should be something like:
T RemapDeclaration<T> (T declaration) where T : BaseDeclaration
It would return the original if it doesn't change. If supplied null, it would return null. If remapped it would return a new instance with the changes.